In some languages, such as French, there is a phenomenon occurring at word junctions that can cause significant changes in pronunciation. This phenomenon is a cross-word co-articulation, referred to herein as "liaison", that is characterized by the optional insertion of a phoneme between two successive words. It occurs when a first word ending in a consonant that typically is not pronounced is followed by a second word beginning with a vowel-like sound. In many contexts, the speaker is free to either pronounce the liaison or not, and is also free to either pause between liaisonable words or not. There is, however, a natural tendency on the part of the many speakers to carry the liaison over into the next word. Optional pronunciations, however, cause ambiguities that are difficult for prior speech systems to resolve.
One solution to this problem may be the generation of a set of rules for each possible occurrence of liaison in the language. A complete set of rules for liaisons is impractical, however, as there are many exceptions and dialectal variations. For example, the French sentence "les deux a la fois" could be pronounced either "les deux a la fois" or "les deux Za la fois". In our terminology, we say that "deux" generates a Z-liaison and "a" accepts a liaison. To our knowledge, no prior system has allowed the insertion of liaisons. Thus, a need has arisen for a speech recognition system that can efficiently handle this common speech characteristic.